SchemaSpy is generating your database to HTML documentation, including Entity Relationship diagrams. I used it for creating documentation for Flexibee database. Flexibee is accounting software and works on postgresql. I recommend follow instruction and tutorial.
I describe steps for Windows 7.
Download Java 8.
Download Graphviz
Add the folder containing Graphviz’s dot.exe application to your system PATH variable, eg.
C:\Program Files (x86)\Graphviz2.38\bin
SchemaSpy is just a single executable jar-file (schemaspy-[version].jar), you can download releases from http://schemaspy.org or the github releases page https://github.com/schemaspy/schemaspy/releases
Download Postgre jdbc
Download a GUI for SchemaSpy
I put all together for better illustration.
Execute schemaSpyGUI.bat
If it doesn’t fit you, there are alternatives:
https://www.dbschema.com/postgresql-designer-tool.html
http://www.elsasoft.com/features_postgresql.htm